1. Field of the Invention
This invention relates to control circuits used for controlling multiple rated motors where the application of the motor requires that the horsepower and torque ratings vary with time.
2. Description of the Prior Art
Multiple rated motors give the user a choice of operating modes so that the most effective operation can be obtained by loads that have variant horsepower and torque requirements during operation. As the load demands vary with time conventional polyphase motors have proven to be less efficient and economical. A varying load can also put additional mechanical stress on the conventional polyphase motors. Multiple rated motors give the user a motor whose speed torque characteristics can vary with the changing demand. However, sophisticated controls are required to shift the motor from one operating mode to another in accordance with the load conditions to attain the more economical and efficient operation.
A reference of interest is a paper entitled "Electric Motor Drives For Oil Well Walking Beam Pumps", written by R. F. Woll, Fellow IEEE, Medium Motor And Gearing Division, Westinghouse Electric Corporation, Buffalo, N.Y. which is copyrighted material of the IEEE and designated Conference Record 76 CH1109-8-1A, Paper No. PC 1-76-33.